1. Field of the Invention
The present invention relates to a doppler radar device used for various meteorological observations, in particular to a doppler radar device using a magnetron as a transmitting tube.
2. Description of Background Art
A burst signal detector circuit of a doppler radar device using a magnetron as a transmitting tube according to a conventional technique is illustrated in FIG. 11. In FIG. 11, numerical reference 410 designates an aerial antenna; numerical reference 420 designates a transmitter; numerical reference 421 designates a magnetron; numerical reference 422 designates a modulator; numerical reference 431 designates a directional coupler; numerical reference 432 designates a circulator; and numerical reference 440 designates a signal processing unit. Numerical reference 441 designates a burst signal detector circuit including a burst gate circuit 141 and automatic frequency control (AFC) 144. Numerical reference 442 designates a trigger generating circuit; and numerical reference 450 designates a receiver including stable local oscillator (hereinbelow referred to as an STALO) 451 and mixer 452.
Next, its operation will be described. In synchronism with a transmitting trigger outputted from trigger generating circuit 442, magnetron 421 oscillates by receiving an electric current supplied from modulator 422. Thus generated transmitted pulse passes through directional coupler 431 and circulator 432 and is emitted from aerial antenna 410. The transmitted pulse reflected by an object is again received by aerial antenna 410, passes through circulator 432, and becomes a received signal. On the other hand, a part of the transmitted pulse is taken out by directional coupler 431, the frequency and phase of the received signal are detected in AFC 144 using the transmitted pulse, generated in a burst gate of burst signal detector circuit 441, and the frequency of magnetron 421 and the frequency of stable local oscillator 451 for mixing are controlled. The received signal is mixed with an output signal from stable local oscillator 451 by mixer 452, and thereafter the mixed is subjected to a phase detection.
FIG. 12 illustrates a control flow of a meteorologic doppler radar using the conventional magnetron illustrated in FIG. 11. A part of pulse to be transmitted, generated by magnetron 421, is divided by directional coupler 431 and received by burst gate 141 in Step 121. In Step 122, it is checked whether or not the divided part is generated in the burst gate, of which temporal position is set in advance. When the pulse to be transmitted is transmitted at normal timing, the transmission frequency and the phase difference are detected by AFC 144, magnetron 421 and stable local oscillator 451 are controlled, observation is started, and data are outputted from the signal processing unit in Steps 123 and 124. In Step 125, when the part is generated outside the burst gate, observation is held on until the operation of magnetron 421 is stabilized and the part is generated in the burst gate. Thereafter, in Steps 124 and 122, observation is started.
In the conventional meteorological doppler radar device using the magnetron as the transmitting tube, a timing of oscillation of the pulse to be transmitted may largely deviate and be generated outside a fixed range of the burst gate because a characteristic of the modulator is affected by the magnetron when a power source is thrown in. Therefore, there are cases that the transmitted pulse is not detected and that the frequency of the magnetron and the stable local oscillator are not normally controlled, whereby an actual application to the meteorological doppler radar is spoiled. Accordingly, it is necessary to wait for observation until timing of transmission is stabilized within the fixed range of burst gate.
Further, when the timing of oscillation of the transmitted pulse deviates or is not stabilized by jitter, xe2x80x9crange 0xe2x80x9d in a system, i.e. a reference time for timing of transmission being a reference timing for observation by radar, deviates, whereby accurate timing can not be measured.
It is an object of the present invention to solve the above-mentioned problems inherent in the conventional technique and to provide a doppler radar device which enables a full-time stable application of a system using a conventional magnetron and a conventional modulator and meteorological observations under various conditions.
According to a first aspect of the present invention, there is provided a doppler radar device comprising: a transmitter for generating a pulse signal to be transmitted; a coupling means for dividing the pulse signal and outputting a part of the pulse signal; a gate means for extracting the outputted part of the pulse signal by filtering through a gate having a predetermined time period; a comparing means for comparing the level of the pulse signal extracted through the gate with a predetermined threshold value; and a searching means for changing a set position of the gate in the gate means based on the result of the comparison, whereby advantages that a system including the doppler radar device is constantly operated under a stable condition even though the conventional magnetron and modulator are used and meteorological observations are enabled under any circumstances, for example, in a time range where a transmitted pulse is unstable by throwing a power source in.
According to a second aspect of the present invention, there is provided the doppler radar device, wherein the transmitted pulse signal is sampled within the predetermined time period in the gate, and a position of the transmitted pulse signal is calculated using the sampling data, whereby the advantages described in the first aspect are obtainable.
According to a third aspect of the present invention, there is provided the doppler radar device, wherein a predetermined gate set range is provided in the searching means, and the set position of the gate is changed within the predetermined gate set range, whereby the advantages described in the first aspect are obtainable.
According to a fourth aspect of the present invention, there is provided the doppler radar device, wherein the transmitted pulse signal is tracked using of a plurality of sampling data obtained in the searching means, whereby the advantages described in the first aspect are obtainable.
According to a fifth aspect of the present invention, there is provided the doppler radar device, wherein an HUNT circuit for manually or automatically moving the set position of the gate outside the predetermined gate set range, whereby the advantages described in the first aspect are obtainable.
According to a sixth aspect of the present invention, there is provided the doppler radar device, wherein the gate is moved to a gate transfer position, registered in advance, by the HUNT circuit, whereby the advantages described in the first aspect are obtainable.